Reference electrode

An electrode with a stable, known potential used as a comparison point for measuring another electrode’s potential. Its potential is defined relative to a specified reference scale.

Electrode potential: The electric potential difference between an electrode and the surrounding electrolyte, defined relative to a reference. A reference electrode provides the comparison needed to measure this potential.
Standard hydrogen electrode: A platinum electrode in contact with hydrogen gas and aqueous solution, assigned a potential of zero volts under standard conditions. It defines the conventional zero point for standard electrode potentials.
Silver chloride electrode: A reference electrode consisting of silver coated with silver chloride in contact with chloride-containing solution. Its compact, dependable construction makes it common in laboratory measurements.
Working electrode: The electrode at which the electrochemical reaction of interest is studied or controlled. Unlike the reference electrode, it is the surface whose potential or reaction is being investigated.
Liquid junction potential: A potential difference that forms where electrolyte solutions of different composition meet. The junction between a reference electrode’s electrolyte and the sample can add measurement error.
Electrochemical potential: The energy change associated with moving a charged species between locations or phases. Electrode potentials express electrical contributions to electrochemical energy differences.
Saturated calomel electrode: A mercury–mercurous chloride reference electrode whose electrolyte is saturated potassium chloride solution. It is a widely used reference with a stable potential, though mercury limits its use.
Counter electrode: An electrode that completes the circuit by carrying current opposite to the working electrode. It carries measurement current, whereas the reference electrode should carry almost none.
Salt bridge: An ion-conducting connection between electrolyte solutions that limits mixing while completing an electrochemical circuit. It maintains ionic contact while helping isolate the reference electrode’s internal solution.
Redox reaction: A chemical reaction involving electron transfer and changes in oxidation states. Reference potentials compare the tendency of redox couples to gain or lose electrons.

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